Emergence and recovery response of phosphate metabolites and intracellular pH in intact Mytilus edulis as examined in situ by in vivo 31P-NMR

We employed surface probe-localized 31P-NMR spectroscopy to examine in situ the impact of short-term emergence (hypoxia) and resubmergence on phosphate metabolites and intracellular pH (pHi) in intact mussels. The use of intact organisms ensured that all intrinsic responses remained active while monitoring of individuals minimized uncertainties resulting from stochastic behavior and other individual differences. The use of a photoetched, balanced-match foil probe combined with 1H-NMR images allowed 31P-NMR spectra to be acquired from the posterior adductor muscle with good signal-to-noise. Upon emergence, all mussels exhibited an increase in [Pi], a decline in [phosphoarginine] and pHi, and very little changes in [ATP] with time. The complementary behavior of [phosphoarginine] and [Pi] indicated a precursor-product relationship involved in the maintenance of [ATP] but the similarity between [phosphoarginine] and pHi time-courses cannot be so readily explained. Irregularity in the time-courses of some parameters could have reflected stochastic gaping activity. Resubmergence responses exhibited a reversal of the emergence responses, except that the pHi eventually became supraalkaline with irregular fluctuations. This might be related to the 'oxygen debt' phenomenon and increased oxidative phosphorylation.